The London Air Ambulance was called to the square at around 7.30pm on Saturday (18 April). A helicopter landed just metres from Nelson's Column and paramedics treated the unidentified woman for 30 minutes. She was then taken to hospital.

The woman's injuries are not thought to be life-threatening and the police say the incident is not being treated as suspicious.

A spokeswoman for the London Ambulance Service said: "We were called at 7.24pm to reports of a person fallen at Trafalgar Square.

"We sent an ambulance crew, a motorcycle responder and London's Air Ambulance team to the scene.

"We treated a woman reported to be in her 20s for a head injury.

"She was taken as a priority to the Royal London Hospital escorted by the doctor from London's Air Ambulance."

Helicopter swoops into Trafalgar Square to save woman who fell from lion: Tourists and Londoners watched in am... http://t.co/QLLDIsh3Yu

Martin Peaple, 26, from Sidcup, who is fundraising for the Air Ambulance, told the Evening Standard: "[The helicopter] started circling above the square, it was coming closer and closer to the ground so I helped clear everyone out of the way. There were a good thousand standing and watching what was going on.

"A lot of people were asking if it was here for a show."

Installed in 1867, the four 20ft long bronze lions were designed by Sir Edwin Landseer and cast by Baron Marochetti.

The Greater London Authority (GLA) has been calling for a ban on tourists climbing the 148-year-old lions due to fears they are being damaged, with potentially dangerous cracks appearing as well as the indignity of having rubbish pushed in their mouths.

The GLA claims the tails of the lions are particularly vulnerable as people use them to climb onto the statues for photographs. One lion is said to vibrate when sat on.

However, English Heritage has opposed the proposal, saying it would prove "deeply unpopular."